When an audio signal is encoded, additional information, such as an envelope, in addition to an actual spectral component may be included in a bitstream. In this case, by reducing the number of bits allocated to encoding of the additional information while minimizing loss, the number of bits allocated to encoding of the actual spectral component may be increased.
That is, when an audio signal is encoded or decoded, it is required to reconstruct the audio signal having the best sound quality in a corresponding bit range by efficiently using a limited number of bits at a specifically low bit rate.